docs: def device_changed(self, old_state, new_state):
          """Mount newly mountable devices."""
          # udisks2 sometimes adds empty devices and later updates them - which
          # makes is_external become true at a time later than device_added:
          if (self._mounter.is_addable(new_state)
                  and not self._mounter.is_addable(old_state)
                  and not self._mounter.is_removable(old_state)):
              self.auto_add(new_state)